Common salt (sodium chloride) is an indispensable nutrient for human beings. For example, common salt plays an important role in regulating the water content and pH of the body, digesting food, nutrient absorption, neurotransmission, and so on. Furthermore, common salt plays an important role in influencing the flavor of foods and drinks. For example, common salt enhances deliciousness and flavor, preserves food, facilitates the production of fermented foods such as miso (fermented soybean paste), soy sauce and bread, imparts texture to paste products and udon (thick wheat flour noodle) noodles, and preserves the color of chlorophyll through stabilization. Therefore, common salt is indispensable for human life, but it is thought that ingesting excessive quantities of common salt raises the risk of conditions such as hypertension, kidney disease and heart disease, although there are a number of views on this. As a result, much importance has been placed on the quantity of common salt ingested, and especially the quantity of sodium ingested, and the reduction of this intake has become a matter of concern. This is not only in order to treat diseases that have already occurred, but also to provide means for preventing healthy people from developing diseases.
In order to reduce the quantity of common salt ingested, one method that has been considered is simply to reduce the quantity of common salt used when seasoning or processing food, but because common salt plays an important role in the flavor of foods, as mentioned above, foods and drinks which simply have reduced quantities of common salt lose flavor and become bland. Therefore, there is a strong demand for the development of a technique that does not diminish the salty taste and flavor of a food or drink having reduced common salt content.
One conventional method for reducing the common salt content of a food or drink without diminishing salty taste or flavor was to use a substance that had an inherent salty taste, that is, use of a common salt alternative. For example, potassium salts such as potassium chloride, ammonium salts such as ammonium chloride and magnesium salts such as magnesium chloride are known as typical common salt alternatives. Furthermore, amino acid hydrochlorides such as glycine ethyl ester hydrochloride and lysine hydrochloride and peptides comprising basic amino acids such as ornithyltaurine, ornithyl-β-alanine and glycyl lysine are also known as common salt alternatives. These salty taste alternatives have the drawback of imparting a bitter, peculiar, or unpleasant taste in addition to a salty taste. As techniques for using these salty taste alternatives to reduce the quantity of common salt used and suppress flavors other than the salty taste that are unpleasant, a seasoning composition obtained by blending specific proportions of potassium chloride, ammonium chloride, calcium lactate, sodium L-aspartate, an L-glutamate and/or a nucleic acid-based taste substance (Patent document 1), and a method for removing the bitter taste of potassium chloride by combining with a calcium salt or magnesium salt of an organic acid (Patent document 2) are known. However, a salt reduction technique that meets users' needs has yet to be achieved for reasons such as the presence of unpleasant tastes in addition to the salty taste and the strength of the salty taste being low.
Furthermore, another method for reducing the quantity of common salt used in a food or drink without impairing salty taste or flavor is to use a substance that enhances salty taste and does not impair salty taste even when the quantity of common salt is reduced, that is, use a salty taste-enhancing substance. There have been many reports of such substances, such as a combination of L-arginine, L-aspartic acid and sodium chloride (Patent document 3), a peptide having a molecular weight of 50,000 Daltons or lower obtained by hydrolyzing collagen (Patent document 4), thaumatin (Patent document 5), protein hydrolysates of various protein materials (Patent document 6), trehalose (Patent document 7), yeast extract (Patent document 8), a peptide obtained by subjecting a protein to hydrolysis and deamidation (Patent document 9) and a taste improver having, as a primary component, a neutral salt obtained by reacting a basic amino acid with citric acid (Patent document 10). However, from the perspectives of common salt reduction effect, flavor, economy and the like, an effective technique that meets consumer demands has yet to be achieved, and there is still a strong need for an effective common salt reduction technique that does not impair salty taste or flavor even when the quantity of common salt used is reduced.    Patent document 1: Japanese Unexamined Patent Application Publication No. H11-187841    Patent document 2: Japanese Unexamined Patent Application Publication No. H04-108358    Patent document 3: U.S. Pat. No. 5,145,707    Patent document 4: Japanese Unexamined Patent Application Publication No. S63-3766    Patent document 5: Japanese Unexamined Patent Application Publication No. S63-137658    Patent document 6: Japanese Unexamined Patent Application Publication No. H07-289198    Patent document 7: Japanese Unexamined Patent Application Publication No. H10-66540    Patent document 8: Japanese Unexamined Patent Application Publication No. 2000-37170    Patent document 9: Publication of the International Application in Pamphlet No. 01/039613    Patent document 10: Japanese Unexamined Patent Application Publication No. 2003-144088